New Phasing HomeLab™ Solutions for Protein Crystallography Structure Determination Using Enhanced Anomalous Scattering Signals

New Phasing HomeLab™ Solutions for Protein Crystallography Structure Determination Using Enhanced Anomalous Scattering Signals

The Woodlands, TX — February 20, 2004. Rigaku today announced the newest member of its family of integrated "home laboratory" single crystal X-ray diffraction solutions. Rigaku's swPhasing HomeLab system allows macromolecular structures to be phased without the need for heavy-atom derivatization or the use of a synchrotron source. A complete and fully integrated package, the Phasing HomeLab is the first and only commercially available product to address the need to solve important structures in circumstances where selenomet homologs of target proteins are difficult to express and/or crystallize, or where heavy atom derivatives are difficult to obtain because the crystals are too fragile. Thus, this product represents an optimized response for leading edge proteomics research where traditional laboratory approaches are inadequate.

Protein crystals may naturally contain, or have incorporated within them, "heavy atom" scatterers which exhibit anomalous scattering in the X-ray region (the bulk of the atoms making up a large protein structure being carbon, nitrogen and oxygen, which exhibit negligible anomalous scattering in the X-ray region for macromolecular samples). In the diffraction experiment, if the energy of an incident X-ray beam is chosen correctly, it can modify the overall contribution of heavy atom scattering to each diffraction spot, and give rise to "anomalous" differences. The information from the anomalous differences can be used to locate the "heavy atom(s)" in the unit cell and thus be used to calculate a unique phase for each reflection and hence solve the crystal structure.

To take advantage of this phenomenon, the Phasing HomeLab employs a brilliant chromium X-ray radiation (2.29 Å) source. With chromium radiation, the contribution to the anomalous term from sulfur is doubled compared to that for traditional copper X-ray radiation. Chromium radiation can also improve the strength of anomalous scattering of many other intrinsic elements in macromolecules, like calcium, zinc, and phosphorus. Furthermore, the anomalous scattering of selenium is increased substantially as well. In effect, using chromium radiation increases the phase information from the sample and in turn yields more easily interpretable electron density maps.

Although, the primary advantages of chromium radiation were recognized some time ago, it was not until the 1980s and 1990s that a new set of exploratory experiments were conducted relative to phasing protein structural data. However, application of this powerful technique has heretofore been limited because of lack of suitable laboratory X-ray generators and optics capable of providing intense monochromatic Cr radiation. Now, together with integrated He-purged beam paths to minimize attenuation, LN2-free cryo-cooling to inhibit radiation induced crystal damage, and advanced software for phasing, the barriers restricting broad adoption of this approach are now removed.

Perfect for investigators who wish to increase the throughput of de novo structure solutions in their home laboratory, the Phasing HomeLab consists of an X-ray generator, optics, a goniometer, a choice of detectors, and a cryogenic crystal cooling system. The X-ray source is a combination of the new Osmic VariMax™ Cr optic together with a MicroMax™-007 rotating anode generator. For detection, either an R-AXIS IV++, or the high-throughput R-AXIS HTC, is provided. Both of these imaging plate detectors feature large 300 mm by 300 mm apertures and unique He(g) beam paths to reduce atmospheric absorption of the signal. In addition, a LN2-free X-stream 2000™ low temperature system is provided to mitigate the effects of radiation damage to delicate protein crystals. For data acquisition and reduction, CrystalClear and either d*TREK or HKL2000 are offered, with both software packages incorporating empirical corrections necessary to correct for sample absorption.

Rigaku—Leading With Innovation

Since its inception in Japan in 1951, Rigaku has been at the forefront of analytical and industrial instrumentation technology. Rigaku and its subsidiaries form a global group focused on life sciences and general purpose analytical instrumentation. With hundreds of major innovations to their credit, Rigaku companies are world leaders in the fields of small molecule and protein crystallography, X-ray spectrometry and diffraction, X-ray optics, as well as semiconductor metrology. Rigaku employs over 1,100 people in the manufacture and support of its analytical equipment. Its products are in use in more than 70 countries—supporting research, development, and quality assurance activities. Throughout the world, Rigaku continuously promotes partnerships, dialog, and innovation within the global scientific and industrial community.

For further information, contact:

Joseph D. Ferrara, Ph.D.
VP Product Marketing and CSO
Rigaku Americas Corporation
Tel: (281) 362-2300
eMail: Joseph D. Ferrara